1. Field of the Invention
This invention generally relates to spectrometers. More specifically, the present invention concerns a portable reflectance spectrometer that is capable of being manually carried for use in obtaining spectral data at remote geographical locations.
2. Description of the Prior Art
Satellite technology today makes possible geographical surveys of the earth's surface by means of satellite-carried systems. As an example, the earth resources technology satellite (ERTS) produces images of the earth's surface in four spectral bands with an instantaneous field of view of approximately 79 meters, i.e., the approximate size of a football field. As a further example, the Skylab multispectral scanner produces images in thirteen spectral bands with a picture element size generally similar to that of the earth resources technology satellite.
Direct identification of earth materials by using spectral methods requires that satellite images be calibrated to one or more known points within the image.
To get a true measure of the average spectral reflectance for an area covered by a picture element, as many as 100 spectra are required to obtain a statistical average of the reflectance for an area. The effects of varying atmospheric transmittance and sky radiance also must be accounted for during a spectral scan. It is highly desirable to have a portable spectrometer which is manually portable so as to be capable of being used in a light aircraft or best of all manually carried to remote areas covered within a picture element being simultaneously surveyed by a satellite-carried system. With such a manually portable spectrometer, true values for the reflectance for a calibration area of a picture element can be determined from data obtained at or near ground level. It would then be possible to readily design image processing procedures to effectively normalize image data to the calibration area and make accurate determination of rock and soil types at other points in the picture covered by the satellite-carried system. This is particularly important in the area of searching for particular mineral deposits and/or areas of hydrothermal alteration and the like.
The prior art includes numerous different types of spectrometers. Prior art reflectance-type spectrometers, however, have generally not been suitable for use in obtaining measurements in remote areas, for the reason that such systems have been extremely complex and large, typically being required to be transported in trucks and/or vans. Accordingly, spectral data for remote areas has not been heretofore readily obtained at ground levels. Moreover, typical prior art spectrometers have been limited to use for a narrow spectral range generally spanning approximately a third of the spectral range covered by the subject invention.
Accordingly, the potential for accurate accumulation and recordation of spectral data has been in the past severely limited and has effectively denied scientists the ability of properly analyzing the vast amount of information that is actually obtained through the ERTS satellite and similar satellite-carried systems.
It is, therefore, the intention of the present invention to provide a portable reflectance spectrometer which is capable of being readily manually carried such that accurate spectral reflectance information of remote areas representing calibration areas can be obtained to enable the valid interpretation of spectral picture elements obtained by satellite systems.